In the recent years, nanotechnology has gained importance and has become one of the major research focus areas for its fundamental and practical applications. The smaller size of the particles especially less than 100 nm is one of the key parameters that is responsible for various properties such as electronic, electric, optical, magnetic chemical and mechanical properties that makes nanoparticles suitable for several applications in the fields of ceramics, catalysis, coatings, electronics, chemical and mechanical polishing, data storage, fuel cells, etc.
Many commodity and specialty chemicals and materials such as carbon black, titania, silica and zinc oxide are produced in the form of fine particles, which find applications in a wide variety of industrial and domestic products ranging from tyres, printing inks, paints and pigments, plastics, optical fibers, catalysts, pharmaceutical ingredients and cosmetics.
For many practical applications, it is desirable to have particles of small size as well as of narrow size distribution because smaller particles with narrow size distribution result in better properties of finished products. For example, activity of catalysts, hardness and strength of metals, electrical conductivity of ceramics improve as the particle size decreases.
These special properties of the nanoparticles can vary markedly from those of the analogous bulk materials. The physical and chemical properties of the nanomaterials tend to be exceptionally dependent on their size and shape or morphology. As a result, materials scientists are focusing their efforts on developing simple and effective methods for producing nanomaterials with controlled particle size and morphology and hence, improving their properties.
Many techniques and methods have been employed for the synthesis of nanoparticles on the laboratory scale. Some of the well known methods and systems are as follows:                a) Gas phase synthesis process: It is one of the routinely employed techniques used for large scale production of nano powders, as it is a single step process without any moving parts and any extensive solid-liquid separation processes.        b) Chemical and mechanical routes such as microemulsion-based synthesis and grinding.        
Amongst the above mentioned methods and techniques, flame aerosol synthesis is one of the commonly and widely used technologies for synthesis of fine powders on an industrial scale, as it offers many control parameters like flame temperature, flame structure, stoichiometry, pressure level, residence time distribution, turbulence etc.
The typical method of synthesis of nanoparticles in flame aerosol synthesis is as follows:                a) Injecting the precursor or reactant into the reactor in the form of a vapor or liquid using a carrier gas along with air and fuel.        b) Chemical reactions occur in the gas phase in the flame at high temperatures and results in product molecules;        c) Growth of the particles by coagulation and/or surface reaction to form product particles due to decrease in the temperature at downstream in the reactor        
The temperature decrease at the downstream of the reactor results in the particle growth mainly by coagulation and results in irregularly structured particles and particle distribution.
Further, the powders produced in the aerosol flame reactors have a relatively large particle size and have wide size distribution, with particle size ranging from a few nanometers to micrometers, the wide particle size distribution is influenced by several factors, namely, burner geometry, nature of flame and its configuration, inlet reactant flow rate and its concentration, and turbulence characteristics, gas and particle velocities, pressure and temperature profiles and residence time distribution inside the reactor.
Yet another challenging task lies in scaling up of the process to produce nanoparticles in large quantities, while at the same time maintaining the particle size in the nanometer range.
Hence, there is a need for controlling the product particle size distribution by manipulating and designing the process input variables.
Further, there is also a need for scaling up the process of synthesis of nanoparticles with desired characteristics.
Some of the prior arts that propose a system, method and scale-up process for synthesis of nano-particles are as follows:
U.S. Pat. No. 5,498,446 (Axelbaum et al) teaches a method and apparatus for reacting sodium vapor with gaseous chlorides in a flame to produce nanoscale particles of un-oxidized metals, composites and ceramics. The flame is operated under conditions which lead to condensation of a NaCl by-product onto the particles. The condensate encapsulates the particles and aids in controlling desired particle size and preventing undesirable agglomeration among the particles during synthesis. Following synthesis, oxidation of the particles is inhibited by the encapsulation and handling character of the products is greatly enhanced. Though the '446 patent discloses a method and apparatus for synthesis of nanoparticles, it does not disclose the means for optimization, and controlled particle size distribution of nanoparticles. Further, '446 patent does not address challenging aspect for the scale-up of production of nanoparticles with the desired particle size.
EP 1122212 (Hendrik et al) teaches a method to control particle characteristics of flame made nanostructured powders and investigated at high production rates addressing the required safety concerns. The influence of increasing the fuel and production rate, burner configuration and total oxidant flow on particle size morphology and composition is presented for synthesis of silica in a commercial oxy-hydrogen burner. Hence, the patent application discloses a method to control particle characteristics of flame made nanostructured powders experimentally, which is expensive and time consuming.
“Computational fluid-particle dynamics for the flame synthesis of alumina particles” by Johannessen et al (2000) discloses a mathematical model for the dynamics of particle growth during the synthesis of the ultra fine particles in diffusion flame. The article combines a simple batch model for coagulation and coalescence of aerosol particles along with the computational fluid dynamics model (Fluent) in a decoupled manner to simulate the gas composition, temperature and velocity profiles in a flame reactor and integrate the simple monodisperse population balance (MPB) model along a set of “characteristic trajectories” only and not for the entire flame structure. Further, the article discloses the computational fluid-particle dynamics for the flame synthesis using specific burner with three concentric quartz tubes. Further, the article does not determine the particle characteristics throughout the reactor and does not determine the particle characteristics using various burners and does not address the challenging aspect for the scale-up of production of nanoparticles with the desired particle size. Further, the simple kinetics used in the article only applies for a limited range of temperature and particle size.
Thus, in light of the above mentioned prior arts it is evident that there is a need to have a customizable solution for optimizing and controlling the particle size distribution in a continuous process rather than a batch process and scale-up of production of nanoparticle in an aerosol flame reactor.
Further, there is a need to have a customizable solution to optimize and control the particle size distribution and scale-up of production of nanoparticles in aerosol flame reactor in a coupled manner i.e. by solving the particle dynamics equations in each and every cell of the computational domain.
It is also evident that the process equipment design and scale-up, pilot scale studies are tedious and expensive. Hence, there is growing demand to have a customizable solution for synthesis and scale-up of nanoparticles with desired particle size and shape by improving the process design and scale-up which provides the basic process understanding and dynamic behavior of the flame reactor to reduce the efforts on pilot plant studies for the synthesis of any material.
In the present invention we propose a novel approach for optimizing and controlling the particle size distribution and scale-up of production of nanoparticles in aerosol flame reactor to overcome the above mentioned limitations for synthesis of nanoparticles with controlled particle size, shape and particle size distribution.
In order to address the long felt need for such a solution, the present invention provides a system and method for optimizing and controlling the particle size and scale-up of production of nanoparticles in an aerosol flame reactor, described more particularly herein after.